34 ‘population. The findings also support the program of thyroxine replacement in che exposed Rongelap population to prevent both clinical hypothyroidism andtheassociated rise in plasma TSH, which may be tumorigenic. wassignificantly lower (6.02°1.8 ug/dl). Thefrequency distribution calculations (see Table 29 and Figure 39) indicate that a substantial portion ot the Utirik population has plasma T, concentra- don <5 yug/dl. Measurements of plasma tri- iodothyronine (not shown) showed similar reductions in those patients with low T,4 values. Plasma During the 1973 survey, T,4 and TSH concen- 40 trations were measured in plasma from 109 unexposed Rongelap and 97 exposed Utirik subjects (see Table 29). The mean Ty, in the unexposed Rongelap group, 7.7 ug/dl, was the same as in March 1973 Group 109 Rongelap unexposed 97 Uurik exposed Plasma T,, pe/dl - Subjects with value <5.0 Subjects with value >IL3 7.72.0 6% 6% 6.01.8" 32%** 6% “Significantly different, 2<~0.001. "*6% had values < 3.8. T ] 7.5 10.0 12.5 RQ. t ‘ ‘ ‘ ‘ \ S r 30 | % oftatal pop ulation Plasma Thyroxine Concentrations (Mean + 5.D.) in Utirik and Unexposed Rongelap Populations, ] March 1973 the plasma T.4 concentrations were skewedto the Table 29 Tr e-—e Rongelap the United States, and, as in the United States, upper range. In the Utirik group, the mean Ty T e---e8 Utirik [ws 4. Thyroid Function in the Utirik and Unexposed Rongeiap Groups 10 25 30 Plasma thyroxine (2¢/100 ml) Figure 39. Percentages of people in Utirik and in Rongelap unexposed groups having given thyroxinelevels, 1973. Table 30 Thyroxine-Binding Globulin (TBG) Levels (Mean = S.D.) in Serum, 1973 TBG by RIA Group Rongelap Exposed Unex All sera All sera* Uurik All sera _ Allsera* capacity mg/dl n pg T,/dl 12 13 29 22 1.450.354 1.822-1.22 1.64+0.95 1.340.45 14 1400 25 21 21.52 69 -25.32215.7 «23.1 ths IS.1= 62 22 1.400.42 1.40--0.42 a TBG-binding n 22 T'BG capacity — 31 27) 18.9 78 «16.4 43 *Omicting sera with TBG>3 or TBG-binding capacity > 30. Statistical comparisons revealed no significant differ- ence ( p>0.05) berween any of the groups. J0bet oI Figure 40. Thyroxine-binding globulin levels in serum and TBG-binding capacity, 1973. 4| | 4